Method and apparatus for removing gas from an alkaline chloride electrolysis cell

ABSTRACT

CHLORINE GAS MIXED WITH BRINE AND IN THE FORM OF FOAM IS WITHDRAWN FROM AN ALKALINE CHLORIDE ELECTROLYSIS CELL WITH A MERCURY CATHODE THROUGH PIPES LEADING FROM A CERTAIN NUMBERS OF ANODES AND ARRANGED ON OPPOSITE SIDES OF THE CELL. THE FOAM IS DELIVERED TO A TANK OR VESSEL WHEREIN THE GAS IS SEPARATED FROM THE BRINE BY DILUTED HYDROCHLORIC ACID AND CENTRIFUGAL ACTION. THE GAS AND BRINE ARE THEN SEPARATELY DISCHARGED FROM THE TANK.

Oct. 3, 1972 os ETAL 3,696,010

METHOD AND APPARATUS FOR REMOVING GAS FROM AN ALKALINE CHLORIDEELECTROLYSIS CELL Filed Aug. 24, 1970 2 Sheets-Sheet l FlG.l

INVENTOR$ Oct. 3, 1972 GLQS ETAL 3,696,010

METHOD AND APPARATUS FOR REMOVING GAS FROM AN ALKALINE CHLORIDEELECTROLYSIS CELL Filed Aug. 24. 1970 2 Sheets-Sheet 2 Q S (mm FlG.2

FIG.3

INVENTORS "F a. 9322 3 WM United States Patent Office METHOD ANDAPPARATUS FOR REMOVING GAS FROM AN ALKALINE CHLORIDE ELECTROL- YSIS CELLFranz Glos, Salzgitter, and Joachim Mischke, Dortmund,

Germany, assignors to Friedrich Uhde G.m.b.H., Dortmund Germany FiledAug. 24, 1970, Ser. No. 66,441 Claims priority, application Germany,Oct. 24, 1969, P 19 53 627.7 Int. Cl. C0111 1/12; B01k 3/00; C22d 1/04US. Cl. 204-99 3 Claims ABSTRACT OF THE DISCLOSURE Chlorine gas mixedwith brine and in the form of foam is withdrawn from an alkalinechloride electrolysis cell with a mercury cathode through pipes leadingfrom a certain number of anodes and arranged on opposite sides of thecell. The foam is delivered to a tank or vessel wherein the gas isseparated from the brine by diluted hydrochloric acid and centrifugalaction. The gas and brine are then separately discharged from the tank.

CROSS REFERENCE TO RELATED APPLICATION Reference is made to the patentapplication of Franz Glos and Joachim Mischke, filed Jan. 10, 1969, Ser.No. 790,337, now abandoned, and entitled Method and Apparatus for theElectrolysis of Alkali Metal Chloride Solutions With Mercury Cathode(Group 114).

BACKGROUND OF THE INVENTION US. patent application, Ser. No. 790,337,now abandoned, describes an electrolysis method, in which the brine isforced into the reaction space between anode and cathode of an alkalinechloride electrolysis cell with horizontal mercury cathode and operatingat high current density. As a result of the artificially createdpressure gradient, the resulting intense flow rate in said reactionspace flushes away the gas bubbles that form at the anode and removesthem from the reaction space by the shortest possible route. Moreover,the anode is constructed in a manner that the bubbles travel to theupper part of the cell not only along the outer anode surface, but alsothrough openings in the anode. In order to achieve the full effectintended by the method and apparatus described in said patentapplication, it is necessary to remove the foam quickly and efficientlyfrom the upper part of the cell. The foam must not be allowed toaccumulate in the upper part of the cell, since otherwise the foam mayeventually cover the entire anode including its bottom surface resultingin a rise of the cell voltage. At low current densities, the gaseouschlorine may be mixed with the foam, whereas at high current densitiesit will entirely be in the form of foam and must be removed from theupper part of the cell quickly and efliciently.

One known method of satisfying this requirement is to suck out the foamfrom the upper part of the cell. The disadvantage of this method is thefast that, as a result, there will be underpressure or a partial vacuumwithin the cell and, in case of a leakage, air will penetrate into thecell. Air acts as an inert gas and will adversely affect the chlorineliquefaction process. A mechanical device is also known, with the aid ofwhich the foam is scooped into so-called foam separators where brine andgas are separated. However, mechanical devices are costly and prone tofaults owing to the corrosive process fluids with which they come incontact, such as chlorine and brine. Such known methods and devices arenot efiicient enough to permit running the cell at a specific load whichis 3,696,010 Patented Oct. 3, 1972 perfectly feasible with metal anodes,i.e. about 30 ka./m. or more. The amount of chlorine gas that will formper unit of cell volume at such high loads is so large that the chlorinegas will be in the form of gas/brine foam with bubbles of extremelysmall diameters.

SUMMARY OF THE INVENTION The present invention provides a method andapparatus that will permit a quick and eflicient removal of foam fromthe upper part of the cell in a simple manner and without the use ofadditional mechanical means, so as to prevent the foam from accumulatingto an extent that the Whole anode is enveloped with foam thus impedingthe formation of gaseous chlorine on the underside of the anode.

According to the invention, the task is achieved by discharging thechlorine gas in the immediate vicinity of the area where it formsthrough a plurality of apertures in each side wall of the cell. Theplurality of apetures in each side wall of the cell for the purpose ofremoving chlorine gas foam are connected to a foam collecting pipearranged along each side wall.

The particular advantage attained through the invention is that theadvantages achieved by the distribution of brine at the anode and theremoval of gaseous chlorine from the anode according to US. patent.application, Ser. No. 790,337, become fully effective, since the foamcan be removed continuously and at the desired rate from the upper partof the cell. The foam discharge pipes at each side wall are arranged insuch a manner that a certain number of anodes are apportioned to eachset of two foam discharge pipes arranged opposite each other.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross sectional view of analkaline chloride electrolysis cell taken substantially on the line 1-1of FIG. 3;

FIG. 2 is a side elevational view of the cell showing pipes leadingtherefrom to a separation tank or vessel; and

FIG. 3 is a top plan view of the cell shown on FIG. 2. DESCRIPTION OFPREFERRED EMBODIMENT The illustrated embodiment of the inventioncomprises an alkaline chloride electrolysis cell in which the brine isintroduced through a supply pipe 1 which has a series of branch pipes 2.The brine enters the reaction space through the hollow stems of theanodes 3, and the anode plates. As will be readily understood, themercury cathode floats on the brine and the chlorine gas collects in theupper part 4 of the cell and flows therefrom through side wall apertures5 from which lead vertical discharge pipes 6. The pipes extenddownwardly and connect to horizontal foam collecting pipes 7 which, asshown, are sectional, the diameters of each section increasing towardthe discharge end. The discharge end of the pipes 7 connect to the upperside of a tank 8 in which the chlorine gas is separated from the brineby addition of diluted hydrochloric acid and by centrifugal action. Thechlorine gas is discharged from the tank 8 through a nozzle 9 at theupper side and the brine flows away through a nozzle 10 at the underside.

It will be seen that the apertures 5 are arranged opposite to eachother. A certain number of anodes are apportioned to each set of foamdischarge pipes 6, which are arranged opposite each other, one for eachside of the reaction chamber.

What is claimed is:

1. A method of removing chlorine gas mixed with brine in the form offoam from an alkaline chloride electrolysis cell which consists infeeding brine to a reaction chamber interposed between separated anodesurfaces and a mercury cathode so that the brine is distributed overeach anode surface resulting in gas-brine foam, gravitationally flowingthe foam through downwardly directed conduits leading from the immediatevicinity of the reaction chamber, and conducting the foam from saidconduits to a gas-brine separating station.

2. A method as claimed in claim 1, which consists in feeding brine fromabove through the anodes, flowing the foam from both sides of thereaction chamber, and joining the two streams of foam in a gas-brineseparating tank.

3. Apparatus for carrying out the method of claim 1,

comprising a housing providing a reaction chamber haveach side and towhich the respective discharge pipes are connected, a tank to which eachcollecting pipe is connected, and gas and brine discharge nozzlesrespectively on said tank.

References Cited UNITED STATES PATENTS 3,535,223 10/1970 Baecklund eta1. 204278 X 3,575,837 4/1971 Shibata et a1. 20499 3,409,533 11/1968Murayama et a1. 204219 3,445,373 5/1969 Schiicker et a1. 204220 X HOWARDS. WILLIAMS, Primary Examiner D. R. VALENTINE, Assistant Examiner US.Cl. X.R.

